Biomass is an accessible and renewable non-fossil-based carbon source that can offer a sustainable alternative to existing fossil fuel-derived transportation fuels and organic molecules. Among the various platform chemicals that can be obtained from biomass conversion, 2,5-furandicarboxylic acid (FDCA) is a key near-market platform chemical that can potentially replace terephthalic acid in many polyesters such as polyethylene terephthalate (PET). FDCA can also serve as an intermediate to other important polymers, fine chemicals, pharmaceuticals, and agrochemicals.
Few studies on the electrochemical oxidation of 5-hydroxymethylfurfural (HMF) using catalytic anodes have been published. Initial studies used noble metals or noble metal alloys (Pt, Au/C, Pd/C, Pd2Au/C, PdAu2/C) as catalytic anodes. (See, D. J. Chadderdon et al., Green Chem., 2014, 16, 3778-3786; and K. R. Vuyyuru et al., Catal. Today, 2012, 195, 144-154.) The highest yield obtained for HMF conversion to FDCA was 83% achieved in a pH 13 solution using black carbon supported PdAu2 alloy nanoparticle electrodes. Sun and co-workers reported several non-noble metal-containing heterogeneous catalytic electrodes (CoPi, Ni2P, Ni3S2, and Ni) that can achieve >˜90% yield for FDCA in a pH 14 solution. (See, N. Jiang et al., ACS Energy Lett. 2016, 1, 386-390; B. You et al., Angew. Chem. Int. Ed, 2016, 55, 9913-9917; B. You et al., J. Am. Chem. Soc., 2016, 138, 13639-13646; and B. You et al., ACS Catal., 2017, 7, 4564-4570.) The kinetics of HMF oxidation increase considerably as pH increases and, as a result, high rates and yields for FDCA production can be achieved at pH 14. However, the stability of HMF decreases substantially as pH increases due to the base-induced polymerization of HMF, which forms insoluble humins. (See, H. A. Rass et al., ChemSusChem, 2015, 8, 1206-1217.)